Can you run faster on the moon?

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This week we're taking on the questions you've waited all summer to find the answers to. We find out whether humans can run faster on the moon than here on Earth, if tea tastes better in china cups, and if talking to plants can help them grow. Plus we look into the world of statistics to learn how many ants it would take to carry a human and discover how many people in the world are having sex right at this moment! Plus, in Kitchen Science, we bring you a watery way to measure upthrust.

In this episode

Novel HIV Vaccine Target Discovered

US Scientists working on HIV have uncovered a viral Achilles heel that might aid in the develop of a vaccine.

Writing in Science, Scripps Institute researcher Dennis Burton and his colleagues have been combing through more than 1800 blood samples from patients in Australia, Africa, Asia, Europe and the US looking for signs of antibodies, termed broadly neutralising antibodies, that can inactivate HIV.

'By first finding antibodies that can inactivate HIV, we can then work out which part of the virus they're targeting and then use that very component as a vaccine,' Burton explains.

Previous attempts to carry out this line of investigation have yielded only antibodies that target relatively inaccessible components of the virus, making it very difficult to incorporate them into a vaccine. But now, with new technology and an updated approach, the team have immediately struck gold with their first patient and uncovered two new antibodies, dubbed PG9 and PG16, which can block the virus from invading and infecting cells.

By making mutant viruses with slightly differing surface structures and testing the newly-discovred antibodies against them, the team have also worked out that PG9 and PG16 target the spike proteins (gp120 and gp41) that decorate the surfaces of HIV particles. The virus uses these spikes like molecular velcro to enable it to recognise and infect immune cells, a process that the antibodies can disrupt.

'Critically,' says Burton, 'the region recognised by these new antibodies is potentially a much more accessible site for vaccine design.' But if people who are infected with HIV are alreading making these antibodies, why are they still carrying the disease?

'Preventing infection in the first place is a very different challenge than ridding the body of established HIV, which integrates itself into the human host's DNA, making it much harder for the immune system to detect. The fact that patients can make these sorts of antibodies - and we got this result from just the first patient we studied - is really encouraging because it suggests that a vaccine should be able to do the same.

So, in someone who is not infected, these sorts of antibodies [produced by a vaccine] should be protective.' The next step will be for the team to continue to use their 'brute force' screening-based approach, now that they know it works, to track down more neutralising antibodies, and the viral sites they recognise, to produce a vaccine that can protect against the widest range of HIV strains.

Steel Velcro

Velcro - or hook loop fasteners, are increadibly useful things. They were inspired by a natural means of distributing seeds such as burrs and have been used for uses varying from holding pockets closed to stopping things floating away in space. However velcro is normally made of plastic so is of limited use in hot conditions, and it has a limited strength.

A group lead by Josef Mair at the Technical University in Munich has developed something rather tougher, steel velcro. Using 0.2mm steel sheets and a carefully designed process of pressing and bending, they've formed something which works just like velcro.

They have a couple of versions - one called Flamingo, which involves holes in one half and sprung prongs on the other half. You push the prongs through the holes and they lock together. They also have the more traditional Entenkopf (duck head) which has groups of steel loops close to each other on one side and barbed prongs on the other, which will catch on the loops.

The velcro can carry up to 7 tonnes per square metre if the weight is pulling the sheets apart and up to 35 tonnes per square metre if it pulls along its length, so it's strong stuff. The real advantage is that it will maintain this hold at temperatures up to 800C so it could be used in assembling cars and other machines more quickly and easily.

Where did all the farmers come from?

Farming and cities seem very much the norm now but in the grand scheme they're actually very recent developments. Modern humans have been around for about 200,000 years and farming has only been with us for the last ten thousand. Farming is a key threshold in human development because once you start farming a piece of land you can support a much greater number of people in a certain area than you would with most hunting and gathering. Although, there are some places in the world where land and sea are so abundant in food you don't need to farm to support lots of people (but that's another story...).

The Near East (that includes Iraq, Iran and Syria) is one place where farming is thought to have originated and later spread through Europe. And there's been something of an argument between academics as to how the spread took place and how it happened so quickly. Some people have argued that farming techniques were rather peacefully communicated through neighbouring populations and that hunter-gatherers gradually gave up their lifestyle and language in favour of the farmers'. But some people argue that the farmers were a specific group of people who out-competed and eventually replaced the native hunter-gatherers in Europe.

Now Barbara Bramanti and her team have taken mitchondrial DNA (mtDNA) samples from three groups. Publishing in the journal Science this week,they took mtDNA from a group of 11,000 year-old hunter-gatherers and mtDNA from some of the earliest farmers. What they found was that these two groups were too distinct to be related. So they then looked at how ancient hunter-gatherers might be related to modern-day Europeans and again, the relationship was almost non-existent.

But it does seem that Central Europeans are descended, at least in part, from these early farmers. So what we can draw from this is that at the end of the last ice age, some people developed farming and they moved most the way across Europe, quite likely displacing the hunter-gatherers. And they think these farmers originated in an area around modern day Slovakia or Hungary but the researchers say they need to do a few more DNA studies to be sure.

So understanding when and why we started farming can tell us something about how we came to live in the cities we do today and also how farming might affect communities across the world which do practise hunter-gatherer lifestyles, e.g. the San in Namibia or Aeta in the Philippines.

Electricians shocked to find out how DNA repairs itself

Scientists in America have shown that cells send electrical signals along their DNA to check its integrity.

If mutations or damage to DNA goes uncorrected, especially if it affects certain critical genes, the results can be disasterous for the viability of cells or whole organisms since one consequence of DNA damage is cancer. Thankfully cells are equipped with enzymes that can recognise genetic spelling mistakes made by mutations and can excise the incorrect letter and replace it with the right one.

But a key question is how this checking process can take place quickly enough, given that the average human cell contains more than 3 billion genetic letters - that's more than a pile of encylopaedias piled taller than a person. To find out, Caltech scientist Jacky Barton and her colleagues used E. coli bacteria to study the process.

E. coli double their numbers every 20 minutes so they also need rapid mechanisms to check their DNA sequence and they also contain the bacterial equivalents of many of the same DNA repair enzymes used in humans, making them ideal study subjects. The researchers focused on two enzymes in particular MutY and EndoIII, which are charged with identifying specific types of DNA damage. These proteins can walk along a DNA chain, checking the sequence, but there aren't very many of them (there may be only 30 MutY proteins in an entire cell) and they move much too slowly to completely screen the genome within the time that they do. But what the researchers also noticed is that these proteins carry with them clusters of iron and sulphur atoms (4Fe-4S), which can pick up and release electrons, changing their charge in the process.

Now, in an elegant series of experiments in which the team made specific molecular tweaks to the structures of some of these repair enzymes, the researchers have shown that the repair enzymes work in pairs and signal to each other using the DNA between them like a telephone line. The process is incredibly simple: one repair protein lands on the DNA and activates itself. A second repair protein lands further along the DNA chain and releases a small amount of electric charge, which is conveyed along the DNA chain as if it were a wire. If it reaches the first protein this indicates that the DNA region separating the two proteins is intact and the sequence is correct. The first protein picks up the electrical charge and detaches from the DNA before binding somewhere else.

But if the sequence is wrong, as a consequence of mutation or damage for example, the signal does not transmit and the two proteins remain attached to the DNA and work their way slowly towards each other, laboriously checking each genetic letter as they go. When a fault is discovered and repaired, signalling between the two proteins is restored and they can depart to screen other parts of the genome. In this way, using electrical signalling, the entire genome can be checked and maintained in tiptop condition by using just a small number of repair enzymes.

Pagerank for Species

Most conservation effort seems to be put into species which are pretty or otherwise attractive to humans, but often there is no point in trying to conserve them if their ecosystem collapses. For example there is no point in stopping anyone killing pandas if the bamboo they live on dies out. In simple cases this result is obvious but in most ecosystems a species depends on, and is dependent upon, many other species. This makes it very hard to predict the knock on effects of loosing a species, without using huge complex computer models.

According to Stefano Allesina and collegues Google's pagerank might hold the answer. This is the ranking system that Google uses to help decide which order to return search results. Basically if a site has lots of other sites linking to it, especially if they are important, then it is probably important too and should appear at the top of the list.

Stefano has been applying this to food webs, so if lions, hyenas, leopards etc all eat a type of gazelle, they will all transfer some of their importance to the gazelle, depending on how much of their diet is gazelle. The gazelle, in turn, transfers importance to the grasses which it eats.

They then used these relationships to rank the species by how much damage they would do if they went extinct, and compared it to other much more complex mathematical models, and found that the results were the same. The Page Rank system is obviously scalable to immensely complex systems - it works for the web, so Stefano's system should work on a food web as complex as they come in the real world, and help conservationists concentrate on the most important species to protect.

How Many Licks...? with Aaron Santos, University of Michigan

Chris - Now, have you ever wondered how many babies are getting born everyday or how many solar panels it might take to power the UK? Well, one man has not only answered these questions but he's also gone on to show us how we can work it out for ourselves. He's written a book and it's called "How many Licks" and it's been published and it's come out this week in the US. It comes out here in the UK very shortly and his name is Aaron Santos and he's a mathematician & physicist of the University of Michigan. Hello, Aaron.

Aaron - Hi. How are you?

Chris - Very well. Thank you. Good to have you with us on The Naked Scientists. So first of all, before we come onto "How Many Licks" and perhaps why it's called that, tell us a bit about yourself and what do you do?

Aaron - Well, I'm a postdoctoral researcher in the Chemical Engineering Department at the University of Michigan and my background is in physics which is basically where I learned to do all these sort of problems, these sort of calculation problems.

Chris - What sort of physics are you doing?

Aaron - I do mostly statistical physics. So, a lot of the things with nano scale systems, a lot of different self-assembly systems and nano particles, and a little bit of biology, but much more just regular straightforward chemistry.

Chris - And so, what led you to come out of the physics world and say, "Right. Let's write a book in which we try and look at some of these complicated calculations about the world around us."

Aaron:: Well it was actually, it was in the middle of my graduate class when I was studying for them and there's a problem that was on the class that was basically, how do you - you have to calculate something that you have no idea how to calculate it first and it's a general problem first originally proposed by Enrico Fermi, and I think the problem he originally used was something like how many piano tuners are in Chicago and this was something that his students were expected to answer by just doing straightforward calculations. So, it just seemed like it would be a good idea to just put a clutch of these problems into a book for math.

Chris - And the name "How Many Licks," how did that come about?

Aaron - Well, there was a commercial. I'm not sure if in the U.K., you guys get Tootsie Roll pops, but it's basically a Tootsie Roll encompassed in a lolly pop and there was a pretty famous commercial back in the '80s about - there was this owl when the cape goes up and he asked the owl, how many licks does it take to get to the Tootsie Roll center of a tootsie pop and the owl basically just takes a bite out of it and says three. So, this was kind of the real answer to that question because that's one of the things what we consider in the book. How many licks would it really take if you were actually going to sit down there and do it?

Chris - Well, one of the other things you've been considering is say, the question, you sometimes see TV adverts where they use scalability and lots of small increments of something, adding up something very big. One of the examples you give in your book is how many ants would you need in order to carry humans. So talk us through that one.

Aaron - Yeah. That's one of the simpler problems in the book. So, it's commonly said that an ant can carry 50 times its own weight and if that's true, how many would you need to actually pick up a human being and just kind of use it to walk you around? Well, ants come in a lot of different sizes. If you look on, I think it's Wikipedia, I think there's a factor of 500 between the smallest ant and the largest ant weight.

Chris - I wouldn't like to guess what the factor is for humans, probably depending on some countries is quite big.

Aaron - Yeah. One would imagine, those countries probably should remain nameless.

Chris - I think our country is between the two of them, probably leading the way actually! So go on. How do we calculate this then?

Aaron - So, if you look at the ants, the ones that are crawling around my apartment, they're about 20 milligrams in mass and if they can carry 50 times their own weight then that means that they can each carry a gram. So, a normal human being is somewhere around 65 kilograms. If I divide 65 kilograms by 1 gram, then you can calculate pretty simply that it's about 65,000 ants that you need to pick up one human being.

Chris - Do you think it's reasonable?

Aaron - I never get into whether things are reasonable or not in the book. I mean, there's a lot of things to consider. First of all, how are you going to fit that many ants underneath you? You either need very large shoes or you need to be lying on your back and then there is some question, whether or not you could even fit that many ants. So, I try to avoid any pretense of reality in any of these calculations. It's not really what we're going for here.

Chris - Now, I got sent an email the other day, Aaron, where someone - it said on there - it said that, "Don't scroll down until you've read the top line" and then it said, "Around the world, about 35 million people are having sex at this precise moment." And it said "Now scroll down, now scroll down, it set apart from one old timer who's currently reading his emails." So, how many people are currently engaging in sexual congress right now then and how would you calculate something like that?

Aaron - I should say before I answer this one that I answered a similar question in a talk that I gave once. And was heckled mercilessly by a woman in a crowd who was convinced that the percentage of time that I thought people were actually having sex was much too low. So, you might get a few angry calls in from this but...

Chris - We won't judge it by your own standards Aaron. It's all right.

Aaron - Okay. So to do a problem like that, you'd want to say, "Alright, well how often does a normal person have sex and this clearly depends on what type of person you are." If you're a priest, it's going to be much rarer than if you were in a committed relationship in your early 20s. But the number I used to calculate this one, it was, I'd say once every three weeks seemed like a reasonable number. You're certainly not going to be having sex once every day, at least not by my lifestyle. And once a year seems much too long, so once a week seems like a good compromise. And then you say well alright, how long does a typical sexual encounter last and then it depends on do you count foreplay, do you count what counts as a sexual encounter. But I thought, 15 minutes seems like a reasonable amount of time for that. So, that gives you...

Chris - People here in the studio are nodding. They think that's okay.

Aaron - Okay good, good. Although I have to say that the people that I have generally asked these questions to tend to be scientists, so I think my results might be a little skewed, but you guys fit that demographic. So, maybe that's why you guys are nodding in agreement. But that would be 15 minutes out of three weeks, so you could calculate that that's about 0.05% of the time and then if that percentage also applies to the number of people that are having sex, then it's just 0.05% of the population which would be about 3.3 million people.

Chris - So also my estimate was far too high. My email that I got then was ten-fold too high probably.

Aaron - It could be or I could have messed up on one of the numbers that I gave you, but I would question the email more than the numbers because I at least know where those are coming from.

Chris - But the point of all this is that it's basically showing people how you break down a big complicated problem which scientists frequently encounter into a series of small steps and make a few small assumptions in each step in order to arrive at a ball park sort of figure.

Aaron - Exactly. I mean, you want to start with the things that you know how to do first. I mean, you don't want to just guess at the number of people having sex because you could be way off with that. But if you start doing things that you are familiar with and then just multiplying them together then usually, you can come up with something that's pretty close.

Weighing Buoyancy

Does Shaving make hair grow faster?

Diana - Well, the short answer is no. We had a really good answer from the forum about this actually from databit who said that hair grows actually in a cone shape. So, when you let it grow naturally, the end looks thinner and therefore, the hair looks thinner. But when you actually shave it, you cut it right at the base where it's at it's very thickest and that makes it look much thicker. So, once you've start shaving your hair, the stubble will look much thicker and make it look like more like it's actually growing, but there isn't. It's the same.

Chris - And the other point I think also to make is that when you're cutting a hair that is growing already, it's got a head start because it's already an actively growing hair compared with a hair follicle that was not active because hair follicles go through various cycles of activity and inactivity. So therefore, you're cutting a growing hair already therefore, it's already growing. Therefore, it's going to grow back quicker.

Diana - That's right. You sort of bring all the hairs back down to the same level of growth and so, it appears as if they're all sort of growing at once.

Can you run faster on the moon?

Dave - On the moon, the gravity is about a sixth of the earth so you can jump much, much higher. Whether this helps you with running, it depends on what kind of running you're doing, I think. If you're trying to sprint, if the sixth amount of gravity then you're going to have a sixth of the amount of friction between your feet and the floor because friction basically goes at how hard you're pushing against the floor, and this means - but your mass is still the same, so you still need the same force to accelerate. So, he'll be able to accelerate about a sixth of the rate as he could do normally. So, in a 100-meter sprint, he's almost certainly going to be a lot slower. But if you're running a very long way, you could probably get an advantage because you can take huge strides. So, you can sort of - you could take a huge stride and then not do anything for a three or four seconds while you fly through the air and then you can land and do a little bit of exercise and fly through the air for a bit. So, you get some time to recover in between so I think you could probably run long distances faster, but short distance is not maybe as quickly.Diana - So, it'd be like the laziest race ever then, wouldn't it basically?Dave - Oh, it depends how fast you're going but, yeah.

What is Limonene?

Chris - Brilliant. Yeah, well limonene, it's the stuff that makes oranges and lemons smell orangey and lemony. So, if you take an orange and you scrape the peel a little bit and smell your fingers, it's that very intense orangey citrus smell, isn't there?Don - Yeah.Chris - And that is the limonene. The orange peel contains huge amounts of it. It's a very big organic molecule. It's lots of carbon and hydrogen atoms stuck together in giant ring structures. And in fact, we did an experiment on The Naked Scientists a little while back. Dave did it as a Kitchen Science where you actually blasted some of the limonene through a candle by squeezing the peel of the fruit and you spurted the limonene into the flame.Dave - That's right. You produce a sort of aerosol of limonene into the flame and limonene is really flammable and so, it catches fire.Chris - But the reason that fruit makes it is because it's also quite nasty for things other than humans who haven't got fingers to peel an orange. If you try to borough through the peel of an orange, you'd have to eat the peel and the peel doesn't taste too good. Limonene is mildly toxic and being organic and unpleasantly tasting as it is, it puts off insects and that's a way that the tree uses of keeping its fruit in good condition.Don - Okay. I find it also in my shower gel. Why is it in there?Chris - Sure. Well the answer is rather than trying to invent artificial flavours and colourings and things which would do the same job as a molecule which is already doing the job very well in nature, sometimes it's easier just to use the natural product and then you can also have a marketing benefit because you can say, "Hey! This is a natural product. It's got limonene in it." So, rather than having to use orange flavored stuff or a small molecule that smells the same, then you can just use the natural product and then you get two bangs for your buck. So, what it's doing in your shampoo is contributing a nice orangey aroma and which also, because it's fatty and oily, it will stick to your skin quite well. It won't get washed off by the water and it leaves you smelling vaguely with a faint aroma of oranges. Have you noticed that?Don - Yeah. I have.Chris - Then we've got the answer right. Thank you very much, Don.

Why can light not escape a black hole?

Chris - The point he's making is that a black hole is a collapsed star. So, all the mass of the star ends up in the black hole. So, if light can come out of the star in the first place, given that there's no more mass now in the black hole when it's collapsed, what's changed that now light can't get out?Dave - That's right. When you take a star and convert it into black hole, you actually normally lose an awful of mass. It involves all sorts of explosions and lots of energy given off so that black hole normally weighs an awful less than the original star did, but that mass is much, much closer together - it's much more dense. The force of gravity even the Newtonian force of gravity is essentially proportional to the inverse square. So, if you're twice as far away from it, the force gets four times weaker. So, if you take a star and squash all that mass very close together and then you stand on the surface of it, apart from being burned up and everything, you stand on the surface of it then you're going to be a lot closer, a lot more mass. So the gravity is going to be much, much stronger. And once you go into relativity and general relativity then that mass can bend space enough that light always gets bent around and it can never escape at all, ever.Chris - So, if the black hole blew up again and you took the same mass and put it back to something that was the original size of the star - so in other words, the density was low again then it would start to emit light again.Dave - Yeah then light could escape no problem.

Meera - This week saw the launch of the Centre of the Cell, a new children orientated science center located in the heart of Tower Hamlets and I'm inside the center itself now and it's very impressive, structurally, because it's basically a large orange pod that suspended from the ceiling over a working laboratory. And with me now is the director of the project, Professor Fran Balkwill from Queen Mary University of London. So Fran, tell me more about The Centre of the Cell. What exactly is it and what does it hope to achieve?

Fran - The Centre of the Cell is about inspiring the next generation of scientists and doctors and it's also a unique project, not only because of its location within the working research building, but because it's actually scientists who have led the project and its content has come from over 80 of our scientists.

Meera - And what is the content really? So, what do scientists come up for it?

Fran - The top-level message is that your body is made of millions of tiny cells. When you're real, your cells have gone wrong and scientists in this building and all around the world are trying to find ways to make cells right again and make you better.

Meera - And what would you say the aims of the centre are because it's located here in Tower Hamlets which is not necessarily most affluent of areas. So, that's one of the primary goals of it, isn't it?

Fran - Yeah. It's about raising educational social aspirations. It's about saying to the kids at Tower Hamlets, "You're worth it." It's very much a local project. We've involved 8,000 local children so far in evaluating every stage of the project but it's also got a global reach because we have our website which has had over 10 million hits from 140 different countries and many of the games in the pod are also available on the website. But it is, in terms of the pod itself, it's about bringing in our local young people and inspiring them about science and having a dialogue with them.

Meera - And what would a stereotypical visit then involve?

Fran - It's free. Booking is made online because it's a sort of planetarium type of experience. As children come in, they look down over the research laboratories and they come into the pod. Then there's an opening audiovisual sequence which is about cells and cell biology and then in the middle of the pod, the lighting changes and this amazing structure called the nucleus opens and inside, you find games about cells and cell biologies.

Meera - Now, I'm just wondering around inside the Centre of the Cell and the pod has opened up to a variety of interactive games and I'm here with Esmee from the Petchley Academy. Hello, Esmee..

Esmee - Hello.

Meera - Are you normally interested in science at school or has this helped you to learn?

Esmee - I like science but I prefer more practical science and it helps me learn it. So, I think this is helpful. I mean, it's really interesting, the way it's actually in a laboratory and you can watch real scientists work. It kind of puts into perspective.

Meera - So we've heard the aims of the centre and the opinion of a student visiting it. But is it really educating visitors? Well, Fiona Haddesly-Smith is the Vice Principal of the Petchley Academy. So Fiona, what do you think about the center?

Fiona - I think the most significant thing will be that it is such an interactive set of games that are going on here. And it is very, very interactive, and everything that the students have been learning in the classroom, they can actually take out of the classroom actually use it and see it working in practice. Especially when the students are seeing the scientists working downstairs, so they do realize that scientists have real jobs and it's not just something that me as a teacher teaches in the classroom.

Meera - And would you say then that the games and activities here really do then match what they're doing in their classrooms, so they match the curriculum?

Fiona - They certainly do match the curriculum and I've been looking around and it is absolutely fascinating to see that a lot of the challenges that are presented at Key Stage 3 and actually Key Stage 4 are very precisely addressed here, especially modern science, modern treatments of medicine. Looking at cancer, looking at the way in genes are inherited, looking at the way in which genetical traits are passed on from one generation to the next. And it's really fantastic to see that you're talking now to a real life scientist who is saying the gene for deafness is passed on from one generation to the next. And although I may be teaching that in the classroom, they can actually see it working in action here and that is absolutely brilliant.

Helen - Well, I was invited to come along and to be honest when I walked in, I just kind of stood there and I was going, "Wow! This is cool." I have to hold my hands and to be honest, if you said to me, "Helen, let's go and look at a science lab," I'd think, "Hmm. I'd rather not. That sounds a bit boring." But this is isn't like that. It's full of games, it's full of actual human organs that you can get your nose right up to and I think it just brings it to life and for me, science was always the boring subject at school, but this certainly isn't a boring experience.

Meera - What do you think about the fact that it's hanging, kind of over the labs here at St Barts, do you think that helps the people to see what scientists do?

Helen - Yeah, I definitely do because I think it's easy to go to a museum and you're sort of distant from things then. But actually, what you're looking at is happening right beneath you. And sadly, everybody can relate to cancer or HIV or whatever it is and the fact that there are people working right beneath their feet to combat those things is really quite remarkable.

Can Refrigerators be made more efficient to actually generate electricity?

Peter - Hello. Well, my question is fairly complicated, so you have to bear with me a little bit. We start off with the refrigerator. Now, the refrigerator, actually, you get more benefits than the energy you put in. In the sense that you put a certain amount of electricity and to move heat from the hot to the cold or pump heat away from the cold areas. And you can pump significantly more heat in the energy you put in. So, you got sort of reverse efficiency where you can move several times and probably, I don't know three or four times. I don't know the exact figures. The energy reacted in.Dave - That depends on the temperature you've - the difference in temperature which the fridge is working across.Peter - Yeah, so you're actually moving physically more heat than the energy you're putting in. Now given that, can't we do the same thing in reverse and use the fact that we've created a heat differential to power a heat engine to generate the electricity back again. And now, one or two things will happen. Either will get more electricity out than we should in a sense that we've got an efficiency which is greater than the factor. For an example, let me say, if we pump in four times as much heat and to convert the heat back to electricity, we need only 25% efficiency or better to actually win in the game.Chris - So, this is worth making tons of free electricity just by running your fridge for cooling your beer down, Dave.Dave - Okay, so basically you're asking if a fridge can pump far more heat than the energy you put in, that's definitely true. In fact, if it's pumping for very small temperature difference it can pump 100 times more heat than the energy you put in. Can you make a heat - temperature difference with that and then use that temperature difference in order to generate electricity? We can use that temperature difference to generate electricity, we do use temperature differences to generate electricity all the time. Essentially by using a heat engine - something like a car engine is a heat engine. And basically they can produce high quality electrical energy by moving heat from a hot place to a cold place. But a fridge is essentially just a heat engine running backwards and again with a normal heat engine the amount of energy you can get out compared to amount of heat you can move is to do with the difference between the two temperatures. The bigger the difference in two temperatures, the more efficient it is. And so you'll never, ever going to get more energy out by going around to the circle like this.Chris - You'll just be violating the laws of physics basically, it's just not going to happen. Dave - Yeah, there's a really, really fundamental law of physics. Which essentially says you can't generate useful energy from nothing and this would violate it completely.Chris - It's an analogous question to, if I have a propeller on my car as I drove along, could I connect that to some kind of generator. And then power the car with the generator, it's kind of getting a free lunch isn't it? And it just doesn't happen, energetically speaking it's just not going to happen.Dave - Yeah, and I think actually with this one it would be far, far worse than, it would work far less well than that.

Why does tea taste nicer out of china cups?

Chris - I'd say, it's the placebo effect, wouldn't you? I think it's just because you automatically think it's nicer because it's in glass.Diana - Yeah, having lived, sort of six years on and off as a student, I think it starts to taste the same after a while anyway.Dave - A lot of what you experience from a meal food is to do with the surroundings which is why restaurants spends so much money on having pretty stuff in the room not just on the food.

Can talking to plants make them grow faster?

Chris - The answer is probably not. But I did a bit of poking around, in fact we have covered a story on the Naked Scientists a couple of years ago by scientists (the reference is Meh Jong Jong) in South Korea who published in the Journal of Molecular Breeding.

What they did was to, for some reason - and they don't say why in their paper, they were playing classical music to different plants.

And they tried 14 different types of classical music to see what effect this would have on the plant growth. And the plants, not surprisingly, did not respond at all. So then they thought well perhaps it's a mixture of tones and perhaps plants are sensitive to a range or specific set of tones. So then they started playing sounds at specific discrete frequencies at plants and monitoring gene expressions.

So they would grind up the plant and see which genes have been turned off or turned on in response to the presentation of a tone over a period of time. When they played certain plants a tone at 50 Hz, a series of genes went down, turned off.

When they played the same species of plants some sounds of 150 Hz, 125 Hz or 250 Hz, the same genes increase their activity.

And when they use the molecular machinery, the bits of genetic sequence that turned those genes on and off and link them to another gene, that made the cells change colour, that's called a "reporter gene"; they could, by playing certain sounds to the plants, get these plants to change colour, suggesting that plants are are sound sensitive, so maybe in the case of cereals we know they have ears, so maybe they are sensitive to sounds!

Therefore, maybe, there is some validity in saying you should talk at them. I think it's more likely though, that the CO2 that you are emitting in your breath when you talk to your plants is going to have a bigger effect than the range of frequencies. But maybe Bloke's voices being more low frequency dominate it would have a better effect than women's voices, I don't know.

Diana - So, Prince Charles was right then?

Chris - Maybe Prince Charles is right, maybe.

Dave - Are plants vibration sensitive? Because when wind blows past them they'll vibrate, and if it's windy then they're going to want to have all sorts of different settings, than if it's not..

Chris - Yeah, plants definitely response to being moved around. Because they realize that this is bending them and they therefore need to strengthen and so they deposit more growth related products and then they turn on growth related genes in the other side of the stem to the one in which they are bending. So they strength from the side that they are bending away from. So in other words, it makes it stiffer on that side. And that's why trees can look a little bit bent but still stand up despite say an on shore breeze or something. So that's why.

Why aren't planets compressed by gravity like stars are?

Dave - Well, yeah. Star, it's not actually the fusion which is holding the stars up directly. It's actually their temperature. If you had a gas, the hotter it is the more pressure it will exert, the harder it would push out. So stars are basically supported, they're basically made out of very, very hot gas - plasma that are supported by their temperature. So if a star gets hotter it will expand, star cools down it will shrink. A planet doesn't have to be supported like that, planets are made out of solid, lumps of things they're basically supported by the repulsion between atoms and molecules, in the same way as the table is supported or you're supported. So they are not big enough for the need the temperature to support them and basically just molecules and atoms are strong enough.Chris - Because planets like Jupiter are just around the threshold of what we call brown dwarfs, aren't they, they're failed stars are not quite big enough to squeeze themselves enough to trigger a fusion to actually get going.Dave - Yes, small stars it can also be supported just by this molecular strength basically.

Why is laundry lint always blue?

Diana - That's a good question actually. And now, Dr. Karl Kruszelnicki has worked a bit on on this and he actually did win an IgNobel Prize for his lint research. But he says that for both belly button fluff and laundry lint, is actually an average of all the colours of your clothes. So all the stuff that comes off even your white laundry, will end up being sort of slightly grayish, bluish, horrible colour. And if you think about even if you do have a lot of black clothing, and I'm sure most people will have at least one item of black clothing, will tend to sort of fade to grey and those are the bits that are more likely to disintegrate and fall off and become lint.Dave - It's not always blue. I once washed a bathroom mat from the floor, which was already fluffy and bright red. And that shed completely, it jammed up the whole washing machine and the lint that came out of that was definitely red. Chris - And the other slights a bit of additional information or perhaps you might or might not wants to know about Dr. Karl's study, he actually invited to send in their belly button fluff, to see that colour that was. I think it came out pretty much the same, didn't it?Diana - Yeah, the IgNoble people told him to never, ever do research on this again.

How should or why should a polyester sheet make a fluorescent light bulb glow?

Dave - No, this is perfectly normal. In fact we did a Kitchen Science on this a couple of years back. Basically polyester is a polymer which is quite good at charging up. So if you rub that against your hair or against other sheets it would tend to, as it touches the sheets it would slowly get electrons transfer to it (or away from it, I'm not sure which way with polyester) and so it gained a charge. This means if you move it near a fluorescent tube, a fluorescent tube is basically hollow tube with some very low pressure mercury gas in it. Some of that mercury gas will be ionized, it would've lost electron, you move a charged thing near that some of those ions will move towards or away from the charged thing, will accelerate along, will hit other mercury atoms and knock electrons off those and then you'll get a cascade effect. And get a little bit of electric current flowing through the tube one way, when you take it away then it will flow back again, and that will transfer energy to the mercury atoms some of that they will release as ultraviolet light. This will hit the sort of white coating inside of the tube and that will emit visible light, which you can see as this flash of light. Chris - So there's nothing radioactive about your bed, it's okay then, you're okay.

Why can we not gain immunity to the common cold?

Chris - I wish I knew the answer to that. It's actually just simple numbers. There are two reasons for this. One is to be immune to something, your immune system has to see it in the first place. So you have to be infected with the thing, so you then learn to neutralize it in the future. Now, that would be simple if there was one virus, but in fact there are hundreds.If you look at the rhinovirus family, which is the cause of the common cold, around most of the year, there is about a hundred of those. If you look at the enterovirus family, there's about a hundred of those. There is 50 or 40 adenoviruses, many of which cause upper respiratory and eye infections. Then there are the corona viruses, the parainfluenza viruses, the influenza viruses and to add insult to injury, these viruses also mutate. So not only are there hundreds of them around for you to get your immune system's head around but also they are moving target. They are changing their molecular appearance, so even if you have learned to recognize it, there's no guarantee that you'll recognize it again the next time. And given that there are all these hundreds of viruses and the average person gets about two or three colds per year, that's three life times worth of cold infections before you've actually got any chance of being immune to all of them, by which time they probably have changed.So, I don't think there's really any prospect of ever being able to cure the common cold with the exception that what scientist including Steven Legit who is a researcher of University of Maryland had done, is they've sequenced genetically all of the rhinoviruses so far. And they know how they divide up to a little subfamilies and it might be that if you a made a vaccine based around some members of some of those subfamilies, then every time you immunize someone who gets one of the subfamilies you are protected against all the other members of that family. So you could make a vaccine but it would have probably be based around lots and lots a different members and probably be unfeasible. Who knows, let's hope though that we come up with some kind of common cold cure soon because since you have children you're into a whole different ball game.

Do plants have immunity?

John Carr from the Department of Plant and Sciences at the University of Cambridge:John - Most microbes like bacteria, fungi, and viruses can't infect the plant. But some through evolution, have gained the ability to break down the initial barriers to infection such as cell walls and so on and these can cause disease. Now in response the plants have evolved the ability to respond to and recognize particular types of pathogens. So, that's why some plants have resistance genes and these is a sort of genetic mechanism of allowing them to pass on the ability to fight off particular diseases. Now when this occurs, you might find that the cells which are initially infected with a virus or a bacteria or fungus actually commit suicide. And this is one way of creating a kind of a scorch earth against the pathogen but also it's a way of creating signals, lots more interesting chemicals that float out through the plant tissue. Sometimes plants will produce salicylic acid, it is the parent compound of aspirin and it is a very, very powerful inducer of resistance. So if plants are producing salicylic acid, they are better able to fight off perhaps the first pathogen to attack them unremarkably they're able to fight off possibly lots of other types of pathogen as well. So salicylic acid itself aspirin like compound can give rise to something they call methyl salicylate and this can float off to other plants and influence other plants so they become more resistant.Jonathan Jones, Sainsbury Laboratory, Norwich:Jonathan - Hi, I am Jonathan Jones. I worked at Sainsbury Laboratory in Norwich. Humans have two kinds of immune system, they've got the innate immune system, which recognize molecules that pathogens can help making like flagellum of bacteria for example. And they've got the adaptive immune system which involves antibodies and that's what is triggered when you immunize against viruses for example. Plants and many others sort of less sophisticated organisms have only an innate immune system. They can recognize molecules and pathogens and activate defense. The defense components involve making a sort of bleach - an active oxygen cocktail that inhibits microbes and can culminate in cell death. They also in plants make a lot of anti-microbial proteins that inhibit growth of microbes but also many pathogens squirt proteins into plants cells, to shut down that immune system. And then there's another immune system involving proteins inside the plant cell that recognizes when these molecules show up inside the plant cell and activate defense.